The winner of 31 Grands Prix was the driver steward at Silverstone last weekend, where Fernando Alonso seemed to break through Red Bull's dominance at the half-way point in the 2011 world championship.
Some commentators saw the Spaniard's win as the turning point for the season, despite Red Bull leading McLaren by more than 100 points, while Sebastian Vettel is almost the same margin ahead of Alonso in the drivers' standings.
"The result (in Britain) was great for Ferrari and good for Formula One," Mansell is quoted by Germany's Speed Week.
But he warned: "Red Bull was as strong as ever, second and third, which with its clear lead in the world championship is no problem.
"Red Bull are still going to be very, very difficult to beat," added the Briton.
Red Bull are still going to be very, very difficult to beat
Alonso's Ferrari teammate Felipe Massa agrees.
"My experience in 2008 (against Lewis Hamilton) and Kimi's in 2007 shows that anything can happen," said the Brazilian, "even if this year (winning the title) will be difficult.
"Vettel would have to make a lot of mistakes," added Massa.